The 3rd generation partnership project (3GPP) is responsible for the standardization of the universal mobile telecommunication service (UMTS) system, and long term evolution (LTE) is now under discussion as a next generation mobile communication system of the UMTS system. LTE is a technology for realizing high-speed packet-based communication that can reach data rates of about 100 Mbps on the downlink and about 50 Mbps on the uplink. To this end, schemes and mechanisms are being specified, for example, a scheme to reduce the number of network nodes in conventional UMTS networks. As an example, the macro radio base station in LTE, also known as an enhanced Node B (eNB) or eNodeB will perform the functions of a conventional Radio Access Network (RNC) node and of a UMTS Node B. In addition, eNodeBs in LTE will interact directly with the core network and with other eNodeBs.
An enhancement to LTE, which is also being studied by 3GPP, is known as LTE-advanced. LTE-advanced can reach much higher data rates than the ones used in LTE and an improved coverage. LTE-advanced can also support wider bandwidth as compared to LTE. LTE-advanced is an evolution to LTE and is thus backward compatible with LTE.
In order to improve the coverage of high data rates, group mobility, temporary network deployment, cell edge throughput and/or to provide coverage in new areas, the use of relay nodes (RN) is considered for LTE-advanced. RNs can be deployed in the coverage cell area of a macro radio base station i.e. of a eNB to improve quality and coverage of a network at cell edge where e.g. users or user equipments (UEs) are furthest from eNB.
Although relaying improves the coverage of the eNB, there could be significant interference between the eNB and its subordinate RNs i.e. RNs that are served by the eNB. In the 3GPP technical document denoted R1-090370 and entitled: “Initial Evaluation of Relay Performance” available on the Internet, it is observed that the access link from a low power RN to a UE is significantly limited by the dominant interference from neighboring macro cells. To cope with strong interference between a macro cell and its subordinate RNs, a so-called cooperative silencing can be used as disclosed in the 3GPP technical document cited above. The basic idea of cooperative silencing is to mute macro eNBs in those (preconfigured) sub-frames where RNs are supposed to communicate with their subordinate UEs. A similar scheme named time division multiplexing (TDM) muting was also proposed in a 3GPP technical document R1-091347 entitled: “Relay Impact on LTE System Performance”. A drawback with cooperative silencing and/or TDM muting is that less efficient resource usage is experienced. This is the case for e.g. UEs that can afford some interference i.e. UEs that are close to relays or eNBs.
One way to improve the efficiency in resource usage is to use a scheme known as inter-cell interference coordination (ICIC) instead of using cooperative silencing or TDM muting. The basic idea of ICIC is to apply restrictions to the downlink/uplink resource management in a coordinated way between cells. The restrictions can be in the form of restrictions of what time/frequency resources are available to the resource manager or restrictions on the transmit power that can be applied to certain time/frequency resources. Such restrictions in a cell provide the possibility for improvement in signal to interference ratio (SIR) and cell-edge data rates and/or coverage on the corresponding time/frequency resources in a neighbor cell. In LTE, the standardized X2 interface is available for conveying interference coordination messages, e.g. ICIC messages, between eNBs. However, the messages available on the X2 interface are not suitable for fast coordination on the scheduling time frame partly because of the typical X2 delay characteristics, which are larger than the scheduling interval periodicity of 1 ms, and because of the original design intention of these messages, which targeted a longer time-scale coordination which is longer that the scheduling periodicity. It should be noted that for type-1 RNs which are defined as in-band relay nodes characterized by a serial of characteristics e.g. having its own cell ID, its own scheduler etc., the interference coordination signalling messages i.e. ICIC between type-1 RN and macro eNBs can be exchanged via the X2 interface. However, as mentioned above, the messages available on the X2 interface are not suitable for fast interference coordination because of the delay characteristics of the X2 interface.